Among conventional power supply systems for vehicle, a power supply system for vehicle has been proposed that, upon deceleration of a vehicle, aggressively performs regeneration of braking energy by setting voltage generated by an electric generator which is driven by an engine and feeds power to a battery, to be higher than the voltage upon non-deceleration (acceleration or cruising traveling), and meanwhile, upon non-deceleration of the vehicle, reduces load on the engine to improve fuel efficiency by setting the generated voltage to be lower than the voltage upon deceleration (for example, Patent Document 1).
However, since such a conventional power supply system for vehicle is configured to charge the battery by directly feeding the power generated by the electric generator to the battery, greatly changing the power generated by the electric generator leads to reduction of the life of the battery. Therefore, there is a problem that the range of increasing the power generated by the electric generator cannot be broadened, so that the braking energy cannot be regenerated aggressively upon deceleration of the vehicle.